1. Field of the Invention
This invention relates to a pulse generator for use as a speed detector and more particularly to improvements in the wiring system of a detecting coil.
2. Description of Related Art
FIG. 1 is, for example, a longitudinal sectional view showing the construction of a conventional pulse generator disclosed in Japanese Utility Model Application Laid-Open No. 63-143058. This pulse generator is used for detecting the speed of an automobile, being attached to an automobile transmission case and detecting the rotational frequencies of inner gears. In the fig., the reference character 1 indicates a nearly cylindrical case with a bottom, and within said case 1 is disposed a cylindrical detecting coil 2 wound around a bobbin 3. Centrally at the bottom face of the case 1 is formed a hole having a diameter almost equal to the inner diameter of the bobbin 3. A round bar-shaped magnetic iron core 4 is inserted through both the bobbin 3 and the hole, such that one end thereof is made to outwardly protrude from the bottom of the case 1. Said one end thereof constitutes a detecting head 4a. The other end of the magnetic iron core 4, is diametically expanded, and in contact with a biasing magnet 5 having the same diameter. In addition, upwardly thereof is disposed a spacer 6 for increasing the magnetic flux.
Both ends of the detecting coil 2 are led up to solder tabs 8a, 8a at the ends of two terminals 8, 8 provided upwardly of the detecting coil 2. Other ends of the terminals 8, 8 are formed crimping portions 8b, 8b for crimping lead wires 7, and, by the lead wires 7, 7 crimped there, a signal is outputted toward the outside. The lead wires 7, 7 and the terminals 8, 8 are internally inserted and fixed by a molded element 10. Connections between the upper portion of the detecting coil 2 and the tabs 8a, 8a are wrapped with a tape 9.
The pulse generator arranged as described above is built up in accordance with the following procedure. Both ends of the detecting coil 2 wound around the bobbin 3 are led up to the tabs 8a, 8a of the terminals 8, 8, and then connections between them are soldered. After the connections are taped by means of the tape 9, with a leg 10a of the molded element 10 biasing the magnet 5 towards the magnetic iron core 4 through the spacer 6, the case 1 is inserted and formed. The pulse generator is available in this manner.
The action of a conventional pulse generator will now be described as follows. When, in the passage of a piece to be detected (not illustrated) such as a tooth tip face of a gear with regard to the detecting head 4a, the amount of magnetic resistance change in a magnetic circuit, a portion formed by the magnetic iron core 4, the air-gap and the piece to be detected, reaches the maximum, the change in the magnetic flux in interlinkage with the detecting coil 2 becomes the maximum, and subsequently, the output voltage of the pulse generator then becomes the maximum. On the other hand, when the amount of magnetic resistance change in a magnetic circuit, a portion formed by the magnetic iron core 4, the air-gap and the piece to be detected, reaches the minimum, the change in the magnetic flux in interlinkage with the detecting coil 2 becomes the minimum, and subsequently, the output voltage of the pulse generator becomes the minimum. Consequently, the output voltage of the pulse generator takes the form of an almost sine wave.
With the conventional pulse generator described above, there has been a problem in that tension carelessly applied on the side of wires 7 is instantly transmitted to the terminal 8, forcing the tabs 8a, 8a to instantly and axially move and the end of thin wire of the detecting coil 2 is finally broken there. While the tabs 8a, 8a are taped by the tape 9, in order to prevent the end of a winding from slipping off, there has been another problem in that, tension occurring during winding is inevitably released to slacken the winding, the coil still remains slack even if it is taped by means of the tape 9, and the end of thin wire of the detecting coil 2 is broken due to vibration during the use of it or when it is afterward handled.